CO2 Emissions From Low Order Tundra Streams Stimulated by Surface-Subsurface Connectivity Following Extreme Rainfall Events

Abstract

Increases to summer Arctic rainfall and tundra thermal degradation are altering hydrological cycling in coastal watersheds with implications for carbon (C) cycling and transport of C to the atmosphere and coast. Arctic riverine research has focused on large rivers; however, small streams contribute significantly to vertical and longitudinal carbon dioxide (CO₂) fluxes. Despite the well-established connection between hydrology and biogeochemistry, the impact of extreme rainfall events on Arctic aquatic C cycling remains a knowledge gap. This study characterized how hydrology, biogeochemistry, and geomorphology control the supply of CO₂ to low order streams and their propensity to act as atmospheric CO₂ sources. We characterize biogeochemical and hydrologic processes in unique reaches from a beaded stream and stream impacted by thermal erosion. Rainfall and its resulting increases to terrestrial-aquatic connectivity drove the movement of CO₂ and biodegradable dissolved organic C (BDOC) from soils into streams, however, BDOC mineralization only contributed a small portion of surface CO₂ fluxes. Rain events likely stimulated stream benthic respiration, which led to CO₂ contributions from net ecosystem production often exceeding surface CO₂ fluxes and downstream CO₂ transport. In addition, thermal degradation played a role in terrestrial-aquatic connectivity of the streams. The erosion-affected stream had inconsistent and smaller inputs of CO₂, had weaker heterotrophic conditions, and smaller CO₂ emissions. Understanding how hydrologic regime, influenced by late summer rain events and stream morphology, controls the transport of CO₂ and metabolism in small tundra streams will help improve predictions of landscape scale CO₂ emissions from these critically understudied systems.